1. Field of the Invention
The present invention generally concerns the assembly of (i) any of inorganic substances, molecules, beads, pucks, microspheres and like small things, and also (ii) biological organic (bio-organic) biomolecules, cellular structures, cells and like small biological structures; most typically into patterns on substrates.
Assembly of inorganic molecules may be, by example and not by way of limitation, for the fabrication of large array displays, for massively parallel III-V and II-VI device integration on a different mother substrates, and for heterogeneous integration and pick and place of electronic and/or opto-electronic devices.
Assembly of organic molecules may be, by example and not by way of limitation, for purposes of cell-based biosensors, drug discovery, pharmacogenomics, functional genomics, high-throughput phenotyping, in vitro biology (combinatorial cell culture, signal transduction mechanisms), or any application requiring massive organization of biological cells of any of the plant, bacterial or animal (including mammalian) types.
The present invention particularly concerns the large-scale biocompatible assembly of diverse inorganic and organic materials and molecules having a large range of sizes (typically 100 xcexcm-20 microns) at high yield (xcx9c100%) over but short times (a few seconds) at massive parallelism (for example, so as to realize an array of  greater than 1000xc3x971000 dimension).
2. Description of the Prior Art
The present invention will be seen to involve fluidic-based assembly and/or patterning of small objects, including biological cells, by the combinatorial use of (1) DC electric fields (in an electrical process) in an electrochemical cell having (2) electrodes (2a) at least one of which is selectively patterned (in an optical process), or (2b) at least one of which is selectively patterned by laser light (again in an optical process) where the small objects patterned to one of the (2) electrodes by action of the (ii) DC electric field commonly adhere to the electrode by chemical binding (a chemical process). The present invention will thus be seen to involve each of (1) electrical, (2) optical and (3) chemical processes.
This multi-process, or multi-dimensional, aspect of the present invention is not known to have previously existed, although the individual processes are relatively conventional, and proven.
2.1 Existing Art For Biological Applications
Electrokinetic methods of manipulating cells are described by D. J. Harrison, et al., of Caliper, Inc.
Each of (i) dielectrophoresis, or the manipulating of cells with alternating current fields, (ii) physical methods of localizing molecules and cells (e.g., microfluidics), and (iii) chemical methods of localization (self-assembled monolayers and other specific chemical modifications) are also known in the art.
2.2 Existing Art For Non-Biological Applications
Each of (i) robotic pick and place, (ii) fluidic self assembly, (iii) flip chip bonding, and (iv) probe force microscopy is an established method of manipulating and assembling various small non-organic structures.
2.3 Non-Contact Manipulation
The present invention will be seen to permit non-contact manipulation of small things.
A previous system and method permitting non-contact manipulation of microparticles is shown in U.S. Pat. No. 6,055,859 to Mitome and Tuziuti, and assigned to the Agency Ministry of International Trade and Industry, Tokyo, Japan. This patent for a NON-CONTACT MICROMANIPULATION METHOD AND APPARATUS concerns a method of non-contact micromanipulation using ultrasound. In the method micro particles are distributed in a liquid medium. A ultrasound transducer has a transducer plate, with a surface electrode wholly covering a first principal surface of the transducer plate and with a reverse surface electrode on a second principal surface of the transducer plate. The electrode has a number of short electrode strips arranged in parallel. A reflector is set spaced-parallel in opposition to the first principal surface of the transducer plate at a prescribed distance. A voltage is applied to at least one electrode strip so as to radiate ultrasound, forming a standing wave field between the ultrasound transducer and the reflector which traps the micro particles. The voltage applied to the selected electrode strip is switched to an adjacent electrode strip so as to move the standing wave field by moving the position of ultrasound radiated by the ultrasound transducer, therein moving the trapped micro particles in a direction in which the electrode strips are arrayed.
The present invention contemplates a photo-electrochemical (or, to use an alternative word, an opto-electrochemical) system and method for patterning and assembling of (i) any of inorganic substances, molecules, beads, pucks, microspheres and like small things, and also (ii) biological organic (bio-organic) biomolecules, cellular structures, cells and like small biological structuresxe2x80x94including as may be alive. (For purposes of the present invention, xe2x80x9csmallxe2x80x9d shall mean less than 20 microns in size.) The manipulatable cells include, without limitation by way of lack of enumeration, cells of the plant, bacterial and animal, including mammalian animal, types.
The system and method of the present invention may still further alternatively be describedxe2x80x94albeit arguably less suitablyxe2x80x94as xe2x80x9celectro photo-chemicalxe2x80x9d or even xe2x80x9cchemical photo-electricxe2x80x9d, system and method. The main concept is simply that each of (1) electrical, and (2) chemical, and (3) photo, or optical, processes are variously involved in the invention. In the invention each of these processes (1)-(3) is expressed in an electrochemical, or optoelectrochemical, xe2x80x9ccellxe2x80x9d of many centimeters size, in which xe2x80x9ccellxe2x80x9d the overall method of the present invention is conducted. This cell normally, and preferably, consists of (i) two spaced-parallel planar electrodes, one of which electrodes is sometimes transparent (e.g., ITO glass) separated by (ii) a dielectric fluid containing the inorganic or bio-organic substances and molecules, etc., that are desired to be patterned upon one of the electrodes.
The (1) electrical process transpiring within the cell is perhaps the simplest. Inorganic and bio-organic substances and molecules, and beads, pucks and like small things that are both (i) electrically charged to a first polarity, and (ii) immersed in a fluid transport medium, are patterned by action of moving these inorganic and bio-organic substances and molecules, and beads, pucks and like small things to a patterned electrode of an opposite, second, polarity under force of an applied electric field. Upon first consideration, it seems as if the process of assembling the inorganic and bio-organic substances and molecules, etc., is finished already, there not being much need to consider (2) chemistry nor (3) optics.
However, one or more (2) chemical processes transpiring within the cell can also be important. In the first place, the fluid transport medium is desirably biocompatible, may even be a nutrient solution, when the moved (and patterned) items are bio-organic molecules or cells, including living cells of any of the plant, bacterial or animal types. Secondly, when the patterned materials are organic then, in order to enhance patterning selectivity and efficiency, it is often useful that the patterned electrode should be so patterned not only so as to selectively create electrically conductive regions, but also so as to selectively chemically bind biomolecules. In other words, the electrodes are patterned twice: once with electrically conductive regions and once with chemically receptive (or repulsive) regions. The patterned regions may, or may not, be the same.
For example, agarose gel, as a material broadly non-receptive to biomolecules, may be patterned in, for example, all regions of the electrode except the conductive regions. Moreoverxe2x80x94and similarly to this selective patterning with agarose gel of an electrode that is already patterned with conductive regionsxe2x80x94an electrode that patterned into conductive regions may be further patterned (or re-patterned) in all its regions with still further chemicals so as to selectively accept and bind, or to reject, material that comes, by force of an applied electric field or otherwise, into contact with (patterned) electrode regions, and/or with other regions.
In simplest terms, the (2) chemical processes of the present invention make, insofar as is possible, that the desired material (the inorganic and bio-organic substances and molecules, etc.) within the fluid transport medium will, once transported under force of an electric field between patterned electrodes to desired locations, and only to desired locations, stay in these locations, and only these desired locations, for so long as desired, and only for so long as desired. Differently chemically patterned regions on the electrode may accept, and reject, various of the inorganic and bio-organic substances and molecules, etc. that are all within the fluid transport medium at the same time, or which are within different aliquots of the fluid transport medium successively applied (in a multi-step assembly method). The electrochemical cell with its (1) electrical and (2) chemical processes is sufficient to rapidly (a few seconds per process) reliably (xcx9c100% yield) fabricate from very small objects (typically 100 xcexcm-20 microns) a complete, and permanent, device having high complexity (in accordance with the patterning of the electrode) and massive parallelism (for example, an array of  greater than 1000xc3x971000 dimension).
Involvement of the final (3) photo, or optical, process in the method and system of the present invention comes in two forms. In a more rudimentary and conventional form, photo processes may be used to pattern the conductive regions of the electrode, as by the photolithographic patterning of a photoresist subsequently followed by etching. The same photo processes may also be conventionally used to pattern any chemicals, such as agarose gel, that are applied to the electrode.
In another, optional, use of photo, or optical, processes, however, the present invention contemplates dynamically photo-patterning a photosensitive electrode (which may or may not be pre-patterned with (i) selected electrode regions, and/or with (ii) selected chemical regions) before, or even during, the process of electrochemical deposition. This photo-patterning of a photosensitive electrode, which is preferably made from semiconductor, preferably transpires by passing masked laser light through the other, spaced-parallel, electrode which is transparent, and which is preferably constructed from ITO glass. The photo-patterning, and re-patterning, transpires before each time(s) of, or even during, the electrochemical migration (under force of the applied electric field) of the inorganic or bio-organic substances and molecules, etc. In other words, the inorganic or bio-organic substances and molecules, etc., are patterned to an electrode that is itself dynamically photo-patterned (and/or re-photo-patterned).
This photo-patterning, and dynamic photo-patterning, of a xe2x80x9ctemplatexe2x80x9d electrode to which micro-assembly will be make is, it is respectfully suggested, a powerful concept. When this concept is further coupled with the selective chemical patterning of the electrodes, the present invention offers a powerful method and system for the multi-step assembly of complex objects, including as may contain biomolecules and living cells.
In detail, the photo-patterning is in accordance with the present invention is preferably realized by printing, or patterning, an electrode with laser light. The electrode is preferably so patterned through, and while already assembled spaced-parallel with, another, transparent, electrode; the two electrodes together forming a cell. An appropriate fluid containing appropriate inorganic or bio-organic substances and molecules, etc., is entered between the electrodes; an electrical field is applied; and desired inorganic or bio-organic substances and molecules, etc. are patterned on and to the photo-patterned electrode. The whole process may then be repeated for any of new patterns, solutions, inorganic or bio-organic substances and molecules, etc. Clearly a complex device may be constructed by sequential processes which may be automated and computer-controlled.
1. A Method of Assembling any of Inorganic and Bio-organic Substances and Molecules, and Beads, Pucks and Like Small Things
Accordingly, in one of its aspects the present invention is embodied in a method of assembling any of inorganic and bio-organic substances and molecules, and beads, pucks and like small things, that are capable of holding an electrical charge.
The method consists of patterning any of these inorganic and bio-organic substances and molecules, etc., that are both (i) electrically charged to a first polarity, and (ii) immersed in a fluid transport medium, by act of moving under force of an applied electric field these inorganic and bio-organic substances and molecules, etc. to a patterned electrode having an opposite, second, polarity. The inorganic and bio-organic substances and molecules, etc. accumulate on, and assume the pattern of, the patterned electrode.
The patterning may be of bio-organic substances and molecules, etc. that are negatively charged while the patterned electrode is positively charged, or vice versa.
The patterned bio-organic substances and molecules may, in particular, be any of biological cells of at least the plant, bacterial and animal (including mammalian animal) types, biological molecules including proteins, and/or DNA.
The patterning may be of bio-organic substances and molecules that are alive, in which case the fluid transport medium is bio-compatible.
2. The Assembly Method Extended to Patterning the Electrode Both for (i) Conductive and Non-Conductive Regions, and (ii) Regions of Affinity, or Non-affinity, to Bio-organic Substances, Molecules and/or Cells
In another of its aspects the method of the present invention set forth in section 1 above may be expanded and extended toxe2x80x94at a time and as a step before the patterning of any of inorganic and bio-organic substances and molecules, etc.xe2x80x94patterning the electrode with either or both (i) conductive regions, and/or (ii) chemically receptive or rejecting regions.
Patterning the electrode with conductive regions is preferably conventionally realized by photolithographically pre-patterning a semiconductor electrode with an insulator so that the electrode assumes selected conductive and insulating regions.
This pre-patterning directed to creation of conductive and non-conductive electrode regions may itself be expanded and extended by, at a time and as a step before the photolithographically pre-patterning, further pre-patterning regions of affinity, or non-affinity, to bio-organic substances, molecules and/or cells. This further pre-patterning preferably consists of coating the electrode with a non-stick substance to which bio-organic substances, molecules and/or cells subsequently applied in the patterning step will not stick. (It is alternatively possible to coat the electrode with a substance to which bio-organic substances will stick, or bind.) By this step the photolithographic pre-patterning will also pattern the nonstick substance, leaving an electrode with regions that are selectively receptive, or non-receptive, to bio-organic substances, molecules and/or cells.
The coating of the semiconductor electrode is preferably with agarose gel. Where remaining in non-conductive regions of the electrode after the photolithographic pre-patterning, this agarose gel will cause that bio-organic substances, molecules and/or cells will not stick to these non-conductive regions, which is beneficial for the efficiency and the selectivity of the ultimate electrochemical patterning of these bio-organic substances, molecules and/or cells into, and on, the conductive regions (only).
3. The Assembly Method Still Further Extended to Photo-Patterning (and Re-Photo-Patterning) the Electrode
In yet another of its aspects the method of the present invention set forth in section 1 above may be still further expanded and extended to photo-patterning (and re-photo-patterning) the electrode.
In this variant of the method a cell has a first electrode which is transparent spaced-parallel to a second electrodexe2x80x94which will second electrode become the patterned electrodexe2x80x94that is photosensitive. The preferred photosensitive electrode is a semiconductor.
The photosensitive second electrode may be photo-patterned at a time, and as a step, before any patterning of any inorganic and bio-organic substances and molecules, and beads, pucks and like small things. However, the second electrode may also be photo-patterned during the electrochemical deposition.
A light source like a laser is shined through a mask. The laser light generates electrons and holes on exposed regions of the photosensitive electrode. As a result there will be a larger anodic current in these regions. The excess current of these regions selectively drives negatively charged biological cells, molecules or like small things to these regions. When a patterned mask is used, bio-molecules/devices within the solution will move towards the illuminated on the photosensitive electrode.
In detail, the semiconductor second electrode is preferably photo-patterned (and re-photo-patterned) by selectively exposing it through the transparent first electrode with masked radiation, therein serving to pattern the photosensitive electrode into (i) one or more first regions that are electrically charged to the first electrical polarity and (ii) one or more second regions that are oppositely charged to the second electrical polarity. By this photo-patterning, the subsequent, or concurrent, movement in the electrochemical cell of the inorganic and bio-organic substances and molecules, and beads, pucks and like small things (that are electrically charged to the first electrical polarity) will cause these inorganic and bio-organic substances and molecules, etc. to be attracted to the second region of the patterned photosensitive electrode.
4. An Electrochemical Cell for Assembling Any of Inorganic and Bio-organic Substances and Molecules, and Beads, Pucks and Like Small Things That are Capable of Holding an Electrical Charge
In still yet another of its aspects the present invention may be considered to be embodied in an electrochemical cell for assembling any of inorganic and bio-organic substances and molecules, and beads, pucks and like small things that are capable of holding an electrical charge.
The cell preferably includes a patterned first electrode spaced apart from, and more preferably spaced parallel to, a second electrode by an insulator. A reservoir space formed between the two spaced-apart electrodes contains a solution containing any of inorganic and bio-organic substances and molecules, and beads, pucks and like small things having an electrical charge of a first polarity.
A generator creates an electrical potential between the first and the second electrode, and thus a commensurate electrical field within the solution.
If the patterned first electrode assumes an electrical charge of a second polarity then any of the electrically-charged inorganic and bio-organic substances and molecules, and beads, pucks and like small things that are charged to the first polarity and that are within the solution will migrate towards the first electrode, assuming the pattern thereof.
The patterned first electrode is preferably a semiconductor, and is more preferably silicon.
The second electrode is preferably ITO coated glass.
The insulator is preferably a rubber gasket.
These and other aspects and attributes of the present invention will become increasingly clear upon reference to the following drawings and accompanying specification.